Effect of celastrol on the progression of polycystic kidney disease in a Pkd1-deficient mouse model

Abstract

Aims

Celastrol, a naturally occurring pentacyclic triterpene, has attracted considerable interest because it exhibits potent anti-inflammatory and anti-tumor properties. However, the effects of celastrol in autosomal dominant polycystic kidney disease (ADPKD) remain uninvestigated.

Main methods

We determined the effects of celastrol on ADPKD progression in a novel Pkd1-hypomorphic mouse model by intraperitoneal injection (postnatal day 35–63).

Key findings

Pkd1 miRNA transgenic (Pkd1 miR TG) mice treated with 1 mg/kg/day of celastrol exhibited a lower renal cystic index (by 21.5%) than the vehicle-treated controls, but the fractional kidney weights and blood urea nitrogen levels were not significantly affected with celastrol treatment. At a high dose (2 mg/kg/day), celastrol caused marginal weight loss in the treated mice and had no significant effect on renal cystogenesis, thus indicating a potential toxic effect. We further identified that celastrol increased the phosphorylation level of adenosine monophosphate-activated protein kinase (AMPK) in the cystic kidneys. Moreover, celastrol reduced the renal mRNA expression levels of tumor necrosis factor-α, interleukin-1β, P2RX7, F4/80, CD68, transforming growth factor-β, collagen-1, and fibronectin, which were high in the Pkd1 miR TG mice. Immunohistological analysis revealed that celastrol suppressed macrophage infiltration in the cystic kidneys; however, the renal fibrosis scores and proliferation indices remained high.

Significance

These results indicate that celastrol could be a potent anti-inflammatory agent and a natural AMPK enhancer. However, celastrol has only modest effects on renal cystogenesis and has a narrow therapeutic window. Further studies are needed to clarify whether celastrol has the potential for the treatment of ADPKD.

Introduction

Autosomal dominant polycystic kidney disease (ADPKD) is a common disease, caused by mutations in PKD1, PKD2, and other genes, such as GANAB [32]. Renal function in patients with ADPKD may decline progressively because of the destruction of normal kidney structures caused by the growth of renal cysts [2]. ADPKD pathogenesis involves abnormal cell proliferation, fluid secretion, ciliary signaling, and extracellular matrix defects [31]. Other cellular abnormalities, such as inflammation and metabolic reprogramming, may contribute to cyst expansion and disease progression in ADPKD [15,45]. Inhibition of the cyclic adenosine monophosphate (AMP) pathway by using tolvaptan, a vasopressin V2 receptor antagonist, in patients with ADPKD reduced cyst growth and improved renal function [42]. However, whether a combination of treatments targeting metabolic reprograming, inflammation, and fibrosis are also beneficial in alleviating ADPKD remains unknown thus far [5].

Celastrol and triptolide represent two different classes of compounds that are isolated from roots of the Chinese herb thunder god vine [26,35]. Triptolide inhibits the early phase (up to postnatal day 8) of cyst growth through the suppression of cell proliferation and restoration of cytosolic Ca²⁺ release in Pkd1 knockout mice [[21], [22], [23]]. In an observational cohort of patients with proteinuric ADPKD, treatment with triptolide was associated with a reduction in proteinuria and improvement in total kidney volume [7]. Contrary to those of triptolide, the effects of celastrol on the progression of ADPKD have not been reported.

Celastrol, a naturally occurring pentacyclic triterpene, has attracted considerable interest because it can be used for treating inflammation, cancers, obesity, and autoimmune diseases [3,12,17,20,36]. Small quantities of celastrol are extracted from Tripterygium wilfordii or other members of the Celastraceae (bittersweet) family [10]. Celastrol modulates proteasome activity [48], heat shock responses [38,50], and the nuclear factor kappa B (NF-κB) signaling pathway [18]. Furthermore, celastrol could reduce obesity by sensitizing leptin receptors in hyperleptinemic diet-induced obese mice [25], suggesting that celastrol plays a role in modulating metabolic processes. Therefore, we hypothesize that celastrol is a potential therapeutic agent for ADPKD.

In this study, we investigated the effects of celastrol treatment on renal cyst formation and disease progression in a Pkd1-deficient mouse model of ADPKD. We also determined the effects of celastrol on renal inflammation and fibrosis in the cystic kidneys of the Pkd1 miR mice.